A method of this type is already known from DE 197 00 711 A1.
In a multi-cylinder internal combustion engine, a systematic error in the injection of fuel into the combustion chambers arises as a result of variances, in particular in the mechanical properties of the injection device, for example of the injectors in diesel engines with a common-rail injection system. Due to manufacturing tolerances of the said components and differing degrees of wear (ageing effects), differing quantities of fuel are fed for combustion in the individual cylinders in identical injection periods and under otherwise identical boundary conditions. The differing quantities of fuel lead to a differing output of power by the individual cylinders which, as well as increasing the irregularity in the running of the engine, also leads to an increase in the quantity of harmful exhaust-gas components.
It is known for the irregularity in the running of an internal combustion engine to be analyzed in order to draw conclusions therefrom as to the quantity of fuel injected in the various combustion chambers. For this purpose, for example the angular acceleration of the crankshaft is measured with an engine-speed sensor, said angular acceleration depending on the quantity of fuel injected in each case. Thus a large quantity of fuel injected in the combustion cycle concerned causes a correspondingly large angular acceleration of the crankshaft, whereas a small quantity of fuel injected results in only a correspondingly reduced angular acceleration. This irregularity in the running of the engine is countered in known internal combustion engines by adjusting the quantities of fuel injected in the individual combustion chambers in relation to one another through appropriate activation of the various injectors. In this process, the control signals for the various injectors are altered until such time as all the cylinders make the same contribution to the torque, which indicates that a uniform quantity of fuel is being injected in the various combustion chambers.
This known regulation of irregularities in the running of the engine for synchronizing cylinders in terms of the quantities of fuel injected is restricted in application to low load levels under stationary operating conditions, for example idling. Braking or accelerating, as typically occur in higher operating ranges, could be interpreted incorrectly by the speed sensor on the crankshaft as a difference in the quantity of fuel injected.
The restriction to a low operating point for determining differences in quantities of fuel injected is, however, problematical, since these vary with at least one of the injection parameters, e.g. injection pressure and injection period. The differences in quantities of fuel injected that are determined at a low operating point cannot therefore be used for synchronizing over the whole operating range, e.g. as global correction factors for an activation parameter of the injectors, but have to be adapted to the injection parameters applicable at higher operating points. However, due to the aforementioned requirement for stationary operating conditions for regulating irregularities in the running of the engine, this is not possible without further action.
In the above-mentioned DE 197 00 711 A1, in which correction factors for individual cylinders are applied to the injection period in order to synchronize the cylinders in terms of the quantity of fuel injected, it is proposed that the correction factors determined at a low operating point be adapted by an adaptation factor f(p,t), which is dependent on the injection parameters of pressure and injection period, for higher operating ranges. The values of this adaptation factor are to be stored in an engine characteristics map and taken therefrom for adaptation of the correction factors during operation. While the known method prevents adaptation when the operating conditions are not stationary, it does so only with the aid of a predetermined engine characteristics map whose values cannot optimally match the dependency conditions of the differences in the quantity of fuel injected which exist in reality and which change over the service life of the vehicle.